IP and higher layers (e.g., TCP,
UDP) MUST continue to accept and process datagrams destined to a
deprecated address as normal since a deprecated address is still
a valid address for the interface. In the case of TCP,
this means TCP SYN segments sent to a deprecated address are
responded to using the deprecated address as a source address in
the corresponding SYN-ACK (if the connection would otherwise be
allowed).

=====> What if I have received an echo-request to a deprecated
address.

As per the text I can understand
that IPv6 Accepts the packet and gives to ICMPv6.

However, to send ICMPv6 Echo
Reply it uses the deprecated address is used as